The invention relates to a level control system for a motor vehicle having air springs which can be filled with pressurized air or vented (discharged) to control the level of a vehicle body. The level control system includes a control apparatus which controls (open loop or closed loop) the functions of filling and discharging in dependence upon the level of the vehicle body.
Level control systems of this kind are known from the state of the art for some time and are described, for example, in U.S. Patent Nos. 4,809,957 and 6,332,623. In recent times, more and more, the wish has been expressed by the motor vehicle industry that such control systems should not be used exclusively for controlling the level of the vehicle body (that is, to fill and discharge the air springs) but also for realizing additional functions. One of these functions comprises especially that a reserve or spare tire be fillable by means of a pressurized air source of the level control system via a tire fill connection. This additional function of the level control system makes it possible to configure the reserve wheel as a folding wheel so that less structural space is needed than with a conventional reserve wheel. The savings of structural space is especially advantageous in modern motor vehicles because the structural space available therein becomes ever less. Further additional functions such as preventing the inclination of the motor vehicle when the door is open are conceivable. The additional functions should be triggered via switches which can be actuated either by the driver of the motor vehicle or automatically.
The control apparatus of a conventional level control system is so configured that the function of a level control can be controlled without difficulty thereby. The triggering of additional functions via switches is, however, not easily possible with this control apparatus (for example, the triggering of the above-mentioned function xe2x80x9cspare wheel fillingxe2x80x9d). This is so because additional functions up to now are not provided for and the control apparatus is not designed therefor. Difficulties occur especially when several additional functions are to be integrated into a conventional control apparatus of a level control system.
It is an object of the invention to make a level control system of the kind described above accessible in a simple manner for additional functions.
The level control system of the invention is for a motor vehicle having a vehicle body. The level control system includes: a plurality of air springs which can be filled or discharged with pressurized air to control the level of the vehicle body; a first control apparatus for controlling the functions of filling and discharging the air springs in dependence upon the level of the vehicle body; a second control apparatus; a communications channel for interconnecting the first and second control apparatus; at least one switch for triggering an additional function in the level control system; the switch being movable between a first switching state and a second switching state; the switch being connected to the second control apparatus and the second control apparatus functioning to transmit a signal sequence via the communications channel to the first control apparatus when the switch is transferred from the first switching state into the second switching state; and, the first control apparatus operating to carry out the additional function when the first control apparatus receives the signal sequence.
The invention utilizes the situation that additional control apparatus are anyway present in the motor vehicle and have additional available connections for one or several switches (for example, the control apparatus for the on-board power supply of the motor vehicle).
The advantage achieved with the invention is especially that a level control system (whose control apparatus is designed exclusively for triggering the functions of filling and discharging the air springs and especially has no additional connections for switches for triggering additional functions) can be made accessible in a simple manner for additional functions. It is especially possible to use already specified control apparatus of level control systems which do not per se make possible a triggering of additional functions via switches. Furthermore, a retrofit of existing level control systems with additional functions is possible in a simple manner even when the control apparatus of the level control systems are not suitable for triggering additional functions.
According to a feature of the invention, the additional or second control apparatus is connected to several switches and the respective signal sequences, which indicate a transfer of a switch from a first state into the second state, are different from each other. The advantage of this feature is that the control apparatus of the level control system can detect from the signal sequence which additional function is to be triggered in the level control system.
According to another feature of the invention, the additional control apparatus is connected to a switch for triggering a filling of a reserve wheel by at least one pressure source of the level control system. When this switch is transferred from a first state into a second state, a corresponding signal frequency is transmitted from the additional control apparatus to the control apparatus of the level control system and the additional function xe2x80x9creserve wheel fillingxe2x80x9d is executed there.
According to another feature of the invention, the switch for triggering the filling of the reserve wheel is actuated via a switchable directional valve, which prevents the filling of a reserve tire via a tire fill connection in a base state of the valve and makes possible the filling of the reserve wheel via the tire fill connection in the switched state of the valve. The switch is in its first switching state when the directional valve is in its base state and is transferred into the second switching state when the directional valve is transferred into its switched state. Preferably, the switchable directional valve is actuated directly by the driver of the motor vehicle when the driver wants to fill the reserve wheel (for example, via a switch in the dashboard). The advantage of this feature is that the switchable directional valve need not be driven by the control apparatus of the level control system so that no separate drive channel need be made available (in this way, even conventional control apparatus of level control systems can be used even when these control apparatus are unable to provide a corresponding drive channel).
According to still another feature of the invention, the additional control apparatus is connected to respective switches on the doors of the vehicle which indicate whether the corresponding door is open or closed. The advantage of this feature becomes understandable when one considers the following: when a door of the motor vehicle is opened and the body of the vehicle is at the same time inclined, it can happen that the door strikes the ground and is damaged. When the control apparatus of the level control system receives a signal sequence which indicates which door of the vehicle is open, then, with the aid of the level control system, a possible inclined position of the motor vehicle can be compensated which otherwise could lead to damage of the door (with a switch for a door of the motor vehicle, the additional function xe2x80x9ccheck of the inclined position of the vehicle body and, if required, compensation thereofxe2x80x9d is triggered). The advantage of this feature is therefore that damage of the doors of the vehicle can be substantially avoided.
According to another feature of the invention, the additional control apparatus is connected to a switch for the trunk lid or rear door, which indicates whether the lid or door is open or closed. The advantage of this feature is that the control apparatus of the level control system can undertake a lowering of the vehicle body at least in the region of the trunk lid when it is indicated to the control apparatus that the trunk lid is open and that the vehicle body has exceeded a specific level (accordingly, with the switch for the trunk lid of the vehicle, the additional function is triggered, namely, the function of xe2x80x9ccheck of the level of the vehicle body and, if necessary, lower in the region of the trunk lidxe2x80x9d). In this way, damage to the trunk lid can be substantially avoided (for example, damage because of a collision of the trunk lid against the roof of the garage).
According to another feature of the invention, an additional function can be carried out by the control apparatus of the level control system as long as the switch, which triggers the corresponding function, is disposed in its second state. The advantage of this feature for a switch, which is actuated by the driver of the vehicle (as this can be the case, for example, for the switch for the filling of the reserve wheel), is seen in that the vehicle driver can determine how long the function is to be carried out (that is, how long, for example, the reserve wheel is filled. This is especially advantageous when the reserve wheel is intended to only be partially filled or when a reserve wheel not part of the vehicle or another item is to be filled).
According to another embodiment of the invention, an additional function is carried out by the control apparatus of the level control system over a limited time span. It can happen (for example, because of a short circuit in the switch) that an additional function is triggered in error. The advantage of this feature is that the execution of the additional function is interrupted after the elapse of the time span and thereby damage of the level control system is substantially avoided (for example, by too long a running time of the compressor of the level control system when the additional function xe2x80x9creserve wheel fillingxe2x80x9d is triggered erroneously). It is likewise possible to combine the above two features with each other, that is, an additional function can be carried out as long as the corresponding switch is disposed in its second switching state; however, the procedure can be interrupted after a limited time (when the switch is still in the second switching state).
The communications channel, which connects the additional control apparatus and the control apparatus of the level control system to each other, can be configured in parallel. According to a further advantageous feature of the invention, the communications channel is however configured serially. An advantage of this embodiment is that a series communications channel can be realized especially simply and at low cost. Furthermore, the data transmission via a serial communications channel is sufficiently rapid for the present invention because only small quantities of data need be transmitted over the transmission channel.